Studies will continue on our 2B8 clonal cell line which was derived from normal fetal anterior pituitary tissue. In culture, 2B8 cells produce only prolactin, and we have examined the effects of a number of regulatory agents on the secretory process. Although the 2B8 clonal cells were originally of normal diploid karyotype, they are now hyperdiploid. During the next year we will carry out a number of experiments in which 2B8 cells will be implanted into immature, hypophysectomized rats. We have already found that under certain conditions 2B8 cells can form tumorous masses after subcutaneous inoculation. We will determine the bioassay if the prolactin produced by such tumors is biologically active. The time course of tumor formation will be followed as well as the level of prolactin secreted by the developing tumors. We anticipate that it will be possible to develop a useful model for a variety of studies on hyperprolactinemia.